Powdered thermosetting compositions are widely used in paints and varnishes for coating a wide variety of articles and surfaces. Typically, such compositions provide coatings having a high gloss after curing.
More recently there has been an interest in powdered thermosetting compositions that can provide a matte or low gloss finish. Matte finishes serve a variety of aesthetic purposes including minimizing reflected light, masking substrate defects, and reducing the visibility of dirt. Matte finishes are particularly desirable for military equipment, since a dull matte finish can reduce detection, and for the automobile industry, since matte coatings hide interior trim parts while providing an attractive contrast to high gloss body paint.
Matte powder coatings based on polyurethane chemistry are known in the art. Such coatings employ one or more polyester resins, and a blocked isocyanate as a cross-linking agent. Although low gloss coatings having acceptable mechanical and hardness properties can be obtained from polyurethane-based powder coating compositions, such compositions are considered harder to work with in application lines.
Other matte thermosetting powder compositions are prepared from one or more polyester resin binders combined with either a triglycidyl isocyanurate (TGIC) cross-linking agent, or a β-hydroxyalkyl amide (HAA) cross-linking agent, together with other optional additives. However, outside the U.S., TGIC is considered toxic, and products made using the material must be labeled. Compositions prepared with HAA as the cross-linking agent do not always provide a repeatable, adjustable matte coating with a single set of resins. For example, different combinations of different polyester resins must be used in order to obtain different levels of gloss.
There still remains a need for thermosetting powder compositions that can consistently produce low gloss or matte coatings having good physical properties. There is also a need for thermosetting powder compositions that employ a set of resins that can provide a broad range of gloss levels that are adjustable within a range of less than 1 to about 40 units.